It depends on what you mean by "below."
If you are talking about the area toward the feet (i.e. gallbladder is "below" the liver) the correct terms would be "inferior to" or "sub-" (the gallbladder is subhepatic).
If you are referring to a situation where the patient is in the supine position and "below" means more toward the back, the correct terms would be "posterior to," "dorsal to," or "retro-" (the kidneys are retroperitoneal).
The directional term meaning below a point of reference is "inferior." It is often used in anatomy to describe the position of one body part in relation to another, indicating that it is situated lower or underneath.
The ankle is distal to the knee. The knee is proximal to the ankle. Distal means further from the reference point, proximal means loser to the reference point.
Wrist is the joint distal to the elbow joint.
a point of reference for a measurement
Yes, that is one meaning of "reference point", although the reference point need not be an object, but may simply be a location.
a point of reference for a measurement
The medical term for position above the point of reference is "superior."
No, this would be "displacement" or "motion." Speed is the non-directional scalar quantity (magnitude) for the rate of positional change.
Lateral is a positional term that means away from the midline of the body.
it provides a universal reference point for people that need to communicate, but may not necessarily speak the same languages
height of reference point to determine level
An absolute altimeter is an instrument which measures vertical distance to the surface below a certain reference point.
A point of reference is used in a sentence to provide context or comparison for understanding something. For example, "Using the North Star as a point of reference, the explorers were able to navigate through the wilderness." In this sentence, the North Star is used as a guide or marker for the explorers to help them find their way.